In recent years, interest in the development of low profile, flexible, tunable, microwave antennas for portable applications, such as wearable electronics, biomedical devices and health monitoring sensors, has increased. The characteristics of flexible antennas, such as their ability to conform to a surface and their light weight, make these types of antennas desirable for use in many personal portable devices.
Microwave antennas are commonly fabricated by assembling multiple layers of conducting and insulating materials. Generally, the backside of the antenna is a metal ground plane and the top side of the antenna is a metal radiating element. Sandwiched between the two metal layers is typically a non-conducting, insulating substrate material. Previous researchers have developed flexible antennas by reducing the thickness of the insulating substrate layer or by using only one metal layer. However, the antennas resulting from these fabrication techniques are narrowband and do not meet the wideband requirements of many modern applications.
In most cases, the performance of an antenna improves as the thickness of the insulating substrate material increases. This is particularly true for low profile antennas where the electrical performance (i.e., matching, gain, efficiency, bandwidth, etc.) improves as the antenna thickness increases. Alternatively, from a mechanical standpoint, flexibility of the antenna improves as the thickness of the antenna is reduced. The overall stiffness of the antenna increases with the cube of the substrate thickness and stress increases linearly with the thickness of the substrate, thereby limiting the amount of deflection that is possible before the antenna permanently deforms or breaks. As such, a conflict exists between improving the antenna performance by increasing the thickness of the substrate and improving the flexibility of the antenna by decreasing the thickness of the substrate.
Accordingly, what is needed in the art is a low profile wideband antenna that meets required performance standards while also exhibiting desired flexibility.